1. Field of the Invention
The present invention generally relates to monolithic ceramic electronic components, methods for manufacturing the same, and electronic devices including the monolithic ceramic electronic components. More particularly, the present invention relates to an improvement in the structure of terminals of monolithic ceramic electronic components.
2. Description of the Related Art
A conventional type of monolithic ceramic electronic component, which relates to the present invention, is known as a xe2x80x9cmonolithic ceramic substratexe2x80x9d. The monolithic ceramic electronic component includes a composite body having a multilayered structure including a plurality of ceramic layers.
Inside the composite body, interconnecting conductors are provided to constitute a desired circuit by using passive elements such as capacitors and inductors. Outside the composite body, an active element such as a conductor IC chip and a portion of a passive element as required are mounted.
The resulting monolithic ceramic electronic component is mounted on a desired interconnection substrate and constitutes a desired electronic device.
The monolithic ceramic electronic component is used as an LCR composite high-frequency component for use in mobile communication terminal devices, and as a composite component combining an active element such as a semiconductor IC chip and a passive element such as a capacitor, an inductor, and a resistor, or simply as a semiconductor IC package for use in computers.
More particularly, the monolithic ceramic electronic component is widely used to constitute various kinds of electronic components such as module substrates, RF diode switches, filters, chip antennas, various package components, composite devices, etc.
FIG. 9 is a sectional view illustrating a conventional monolithic ceramic electronic component. A monolithic ceramic electronic component 1 shown in FIG. 9 includes a composite body 3 including a plurality of stacked ceramic layers 2. The composite body 3 is provided with interconnecting conductors each of which is located in association with a particular ceramic layer 2.
The interconnecting conductors are several first terminals 5 arranged on a first end surface 4 in the stacking direction of the composite body 3, several second terminals 7 arranged on a second end surface 6 opposite to the first end surface 4 of the composite body 3, several internal conductor layers 8 disposed at a particular interface between the ceramic layers 2, and several via-hole conductors 9 penetrating a specific ceramic layer 2.
The first terminal 5 is used for forming a connection with an interconnection substrate (not shown). In order to improve the bonding strength with the interconnection substrate, the first terminal 5 includes a conductor layer defined by a conductive paste that is applied by printing.
The second terminal 7 is used for forming a connection with a mounted component (not shown). In order to improve the bonding strength with the mounted component, as in the first terminal 5, the second terminal 7 includes a conductor layer defined by a conductive paste that is applied by printing.
FIGS. 10A to 10E show, in sequence, part of a typical method for manufacturing the monolithic ceramic electronic component 1 shown in FIG. 9. As shown in FIG. 10A, a ceramic green sheet 11, which will form the ceramic layer 2, is formed on a carrier film 10 of polyethylene terephthalate having a thickness of 50 xcexcm to 100 xcexcm. In this way, a composite sheet 12 in which the ceramic green sheet 11 is supported by the backing carrier film 10 is obtained.
During the subsequent steps, prior to a stacking step of the ceramic green sheet 11, the ceramic green sheet 11 is handled in the form of the composite sheet 12.
The reason for working the ceramic green sheet 11 with the carrier film 10 functioning as an undercoat is that the ceramic green sheet 11 has significantly low strength, is soft, and is breakable, and it is extremely difficult to handle the ceramic green sheet 11 by itself. The ceramic green sheet 11 in the form of the composite sheet 12 is easy to handle and to align during the process. Also, undesirable shrinking and undulation of the ceramic green sheet 11 can be prevented during the subsequent step of drying the conductive paste.
Next, as shown in FIG. 10B, several through holes 13 for forming the via-hole conductors 9 are formed in the composite sheet 12. Alternatively, the through holes 13 may be formed so as not to penetrate the carrier film 10 and may be formed only in the ceramic green sheet 11.
Next, as shown in FIG. 10C, by filling the through hole 13 with a conductive paste, a conductive paste section 14 which will be the via-hole conductor 9 is formed. At the same time, the conductive paste layer 15, which will be the internal conductor layer 8 or a second terminal 7, is formed by applying a conductive paste on the outer main surface of the ceramic green sheet 11. Subsequently, the conductive paste section 14 and the conductive paste layer 15 are dried.
Next, as shown in FIG. 10D, after the carrier film 10 is separated from the ceramic green sheet 11, a plurality of ceramic green sheets 11 are stacked so as to define a green composite body 16 which is the composite body 3 before firing.
The separation of the carrier film 10 may be performed prior to the stacking of the ceramic green sheet 11 as in the above description. The arrangement may be such that the ceramic green sheet 11 is stacked in the form of the composite sheet 12, having the surface provided with carrier film 10 facing upward, and the carrier film 10 is separated every time one of the ceramic green sheets 11 is stacked.
Next, as shown in FIG. 10E, a conductive paste layer 17, which will be the first terminal 5, is formed by applying a conductive paste on one end surface of the green composite 16 by printing. The conductive paste layer 17 is then dried.
It should be noted that the conductive paste layer 17, formed after the green composite 16 is obtained, may be used for the second terminal 7 and not for the first terminal 5. In such a case, the conductive paste layer for the first terminal 5 is provided by the conductive paste layer 15 formed by the step shown in FIG. 10C.
Next, the green composite 16 in the state shown in FIG. 10E is pressed in the stacking direction and is fired. Thus, the monolithic ceramic electronic component 1 shown in FIG. 9 is obtained.
The first terminal 5 and the second terminal 7 are plated with nickel and are then further plated with gold, tin, or solder, as required.
Although not shown in the drawings, the monolithic ceramic electronic component 1 is mounted on an interconnection substrate arranged to oppose the first end surface 4 so as to electrically connect via the conductive layer that constitutes the first terminal 5. A component is mounted on the second end surface 6 and is electrically connected with the conductive layer that constitutes the second terminal 7, but this is also not shown.
According to the manufacturing method of the monolithic ceramic electronic component 1 shown in FIG. 10, a step for applying the conductive paste by printing and a step for drying the same must be performed once again subsequent to obtaining the green composite body 16 in order to form the conductive paste layer 17 shown in FIG. 10E. Thus, there is a problem of reduced production efficiency due to these extra printing and drying steps.
It is also possible to use another process in which the conductive paste layer 17 is applied by printing, is dried, and is fired after firing the green composite body 16 in the state shown in FIG. 10D. In this case also, there is a problem of reduced production efficiency as in the above.
Since a screen printing technique is generally used in applying the conductive paste layer 17, reliability of the screen printing from the point of view of precision is not satisfactory. Accordingly, there is a problem of improper formation and displacement of the conductive paste layer 17, smudges in the patterns thereof, and irregularities in the thickness.
When a defective mother composite from which a plurality of the monolithic ceramic electronic components 1 are obtained, is used, all of the resulting monolithic ceramic electronic components 1 may be defective.
It should be noted that during the process in which the conductive paste layer 17 is formed after firing, it is possible to remove the conductive paste layer 17 and perform the printing step again when the above-described problems occur. It is, however, impossible to repair these defects in a process in which the conductive paste layer 17 is applied by printing prior to firing.
Furthermore, during the steps of pressing and firing the green composite body 16, the ceramic green sheet 11 and the ceramic layer 2 tends to be distorted in the direction of the main surfaces thereof. Accordingly, when printing is performed to form the conductive paste layer 17 on the mother composite, the conductive paste layer 17 may be misplaced due to the distortion.
After the step of pressing the green composite body 16, deflection may be found in the green composite body 16 or in the composite 3 after the firing. Thus, the surface on which the conductive paste layer 17 is applied by printing becomes irregular, resulting in the degraded precision of the printing.
Furthermore, the size of the components mounted on the second end surface 6 of the monolithic ceramic electronic component 1 is decreasing. For a mounted component provided with sheet-type terminal electrodes, such as a surface-mounted component, the plane size of each terminal electrode is now reduced to 0.6 mmxc3x970.3 mm. For a mounted component provided with bump electrodes such as a semiconductor IC chip, the size of each bump electrode is reduced to, for example, approximately 70 xcexcm in diameter, and the array pitch thereof is reduced to approximately 150 xcexcm. Accordingly, the conductive layer used as the second terminal 7 must be reduced in size, but the screen printing technique is not capable of forming the conductive layer having such high precision.
Furthermore, an electronic component electrically connected by wire bonding, such as a semiconductor IC chip, is also used as the mounted component. In such a case, the diameter of the bonding wire is approximately 20 xcexcm, and the width of a pad element required for wire bonding is approximately 80 xcexcm. When the conductive layer formed by screen printing is used as the pad element, the cross-section of the thus formed conductive layer shows that there is a beveled part of approximately 20 xcexcm to 30 xcexcm wide at each edge due to surface tension of the conductive paste. Consequently, the flat portion of the pad element 80 xcexcm in width becomes narrow, resulting in joining failure of the bonding wires.
In order to overcome the problems described above, preferred embodiments of the present invention provide a monolithic ceramic electronic component, a method for manufacturing the same, and an electronic device including the monolithic ceramic electronic component, all of which are free of the above-described problems experienced in the conventional art.
A monolithic ceramic electronic component according to a first preferred embodiment of the present invention includes a composite body having a plurality of stacked ceramic layers. The ceramic layers include interconnecting conductors provided in each of the ceramic layers and including first terminals arranged on a first end surface in the stacking direction of the composite body so as to define connections with an interconnection substrate, and second terminals arranged on a second end surface opposite of the first end surface of the composite arranged to define connections with a mounted component. The first terminals include conductor layers provided on the first end surface and the second terminals include exposed end surfaces of terminal via-hole conductors that extend from the inner portion of the composite to the second end surface.
As described above, the first terminal, arranged on the first end surface of the composite body, for providing a connection to the interconnection substrate, is defined by the conductor layer provided on the first end surface. The second terminal, arranged on the second end surface of the composite body so as to define a connection to the mounted component, is defined by the exposed end surface of the terminal via-hole conductor which extends from the inner portion of the composite body to the second end surface.
Accordingly, when manufacturing a green composite body for obtaining the composite body to be accommodated in the multilayer ceramic electronic component, through holes are made in the ceramic green sheets constituting the green composite body, and the conductive paste fills inside the through holes so as to form conductive paste sections which will function as via-hole conductors. The conductive paste is applied merely on one of the main surfaces of the respective ceramic green sheet so as to form the conductive paste layer that functions as a conductive layer.
During the above-described steps, the ceramic green sheet is preferably handled with the supporting carrier film until the stacking step begins. The formation of the through holes and the application of the conductive paste for forming the conductive paste sections and the conductive paste layer can be performed while having the carrier film supporting the ceramic green sheet.
As a result, the precision of printing, for example, for applying the conductive paste is improved, the size of the monolithic ceramic electronic component can be reduced, and density of the interconnections can be increased.
Also, a printing step does not need to be repeated after the green composite is prepared or fired. Thus, failures which may occur during the printing step are reliably eliminated, resulting in a greatly improved yield and reduced cost.
Furthermore, since the second terminal for connecting to the mounted component is constituted by the exposed end surface of the terminal via-hole conductor, the size of the second terminal can be easily reduced, and consequently, the aligning pitch can be reduced. These factors also contribute to the miniaturization of the monolithic ceramic electronic component and increased density of the interconnections.
Preferably, the exposed end surfaces of the terminal via-hole conductors are flat and are arranged on substantially the same plane as the second end surface.
In this manner, the electronic component to be mounted on the second end surface by a surface-mounting technique is prevented from undesirable tilting. The resulting exposed end surfaces are especially suitable for wire bonding and bump interconnection.
Preferably, the interconnecting conductors further include an interconnecting via-hole conductor for providing interconnections inside the composite body and the terminal via-hole conductor has a different cross sectional size from that of the interconnecting via-hole conductor.
In this configuration, it is easy to select a suitable cross sectional size for the via-hole conductors.
More preferably, the cross sectional size of the terminal via-hole conductor is larger than that of the interconnecting via-hole conductor.
In this manner, the area of the exposed end surface of the terminal via-hole conductor which functions as the second terminal is relatively large. Consequently, this configuration is more suitable for mounting an electronic component including sheet-like terminal electrodes and for mounting a metallic casing.
Preferably, the mounted component includes an electronic component having sheet-type terminal electrodes. The surfaces of the terminal electrodes are joined to oppose the end surfaces of the terminal via-hole conductors to fix the electronic component.
Preferably, the mounted component includes a metallic casing that covers the second end surface. The edge surfaces of the metallic casing are joined to oppose the end surfaces of the terminal via-hole conductors to fix the electronic component.
Preferably, the cross sectional size of the terminal via-hole conductor is smaller than that of the interconnecting via-hole conductor.
When the cross sectional size of the terminal via-hole conductor is smaller than that of the interconnecting via-hole conductor, the density for mounting components is greatly improved, and the resulting configuration is more suitable for mounting an electronic component including bump electrodes and an electronic component to be electrically connected by wire bonding.
Preferably, the mounted component includes an electronic component having bump electrodes and the mounted component is joined to the end surfaces of the terminal via-hole conductors through the bump electrodes.
Preferably, the mounted component is an electronic component electrically connected by wire bonding. The mounted component is electrically connected to the end surfaces of the terminal via-hole conductors through bonding wires.
Preferably, a monolithic ceramic electronic component further includes a cavity having an opening along the first end surface.
In this manner, the electronic component can be accommodated in the cavity, achieving further miniaturization of the multifunctional monolithic ceramic electronic component.
A method for manufacturing a monolithic ceramic electronic component according to another preferred embodiment of the present invention includes the steps of preparing a composite sheet including a ceramic green sheet and a supporting carrier film, forming through holes which penetrate at least the ceramic green sheet in the composite sheet, forming a conductive paste section by filling the through hole with a conductive paste, forming a conductive paste layer by applying the conductive paste on the outer main surface of the ceramic green sheet of the composite sheet, separating the carrier film from the ceramic green sheet, forming a green composite body by stacking the plurality of the ceramic green sheets, and firing the green composite body. At least a portion of the conductive paste layers defines the conductive layer constituting the first terminal and at least a portion of the conductive paste sections defines the terminal via-hole conductor.
An electronic device according to yet another preferred embodiment of the present invention includes a monolithic ceramic electronic component, an interconnection substrate for mounting the monolithic ceramic electronic component, the interconnection substrate facing the first end surface of the composite and electrically connected through the conductor layer which constitutes the first terminal, and a component mounted on the second end surface of the composite, which is electrically connected through the end surface of the terminal via-hole conductors.
Because the monolithic ceramic electronic component has a reduced size and allows increased density of interconnections, the electronic device equipped with such a monolithic ceramic electronic component also achieves the same advantages and benefits. The electronic device of this preferred embodiment of the present invention is multi-functional and is greatly reduced in size.
Other features, elements, advantages and characteristics of the present invention will become more apparent from the detailed description of preferred embodiments thereof with reference to the attached drawings.